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One of my oldest Apple MacBook Pro power supplies (about 10 years old) has no issues with the cabling.
However, every other MacBook power supply I have had since has broken within a few years. Essentially the strain relief coming out of the PSU and the strain relief going into the magnetic connector does not relive sufficient strain. Therefore, the plastic sheath around the cable compresses and strains, and eventually breaks. With some power supplies from the last five years, it also seem that the plastic sheath becoming fragile (also near the connector, see below). Here are some pictures of the breaks:
Given that one PSU broke after the other, I didn't feel that shelling out £65 a pop for new PSUs was really good value. Previously I'd tried electric (and other) tape as I am sure many have tried. However, it can overly stiffen the sheath, and usually looks messy after some time.
(Note that these pictures were taken after I removed the 3:1 heat shrink, as well as tape. The tape stayed on for a long time, but started to look quite messy, and didn't seem to provide that much protection - read on.)
2 Enter heat shrink
Strengthening the plastic sheath in the transition from the PSU and to the magnetic connector seemed like a good move, but not with tape. After the tape had only worked for some time, I though I'd try heat thrink.
2.1 Heat shrink 4:1
Initially I'd bough heat shrink with 4:1. The idea being that it would fit over the connector and shrink sufficiently. However, thus resulted in a vey stiff, inflexible jacket. tried to layer the heat shrink, but even only layer is quite stiff.
I initially thought the stiffness might be ok, but one day I bumped the cable again near the treated area and the untreated plastic sheath simply split open, at the transition from the heat shrink to the untreated cable. So that didn't work.
In the picture, you can see the extra break caused.
(Note that I put the heat shrink on with a candle, hence the burn marks. You also can see that the heat shrink runs up to the magnetic connector, but not over it - with this thickness, there isn't enough clearance to do this. Further, you can just about see that the heat shrink went over the existing tape. I thought I would not strain the cable by trying to remove it, so just put the heat shrink over it.)
2.2 Heat shrink 3:1
I then removed the previous heat shrink with a Stanley knife (and great care). As this worked quite well, I also used the knife to carefully remove the tape that I had previously left on. This left the cable as shown in the pictures above.
I then used this heat shrink, with 3:1 ratio:
One size (9mm) fits the older (tubular) connector, while the other size (12mm) fits the newer (T-shaped) connector, in use since about 5 years or so. It's important that the tube is just about big enough to fit over the magnetic connector, but small enough to shrink. (Btw. about 20cm is plenty to fix 2-3 PSUs - of course depending on the damage.)
I simply used a hair dryer to shrink it. This wasn't particularly fast, but worked well, and gave some control. The heat shrink is glue lined, so the glue stuck to the cable in some places, making sure the cable has extra protection. With this type of heat shrink, the cable remains fairly flexible, not putting undue strain either on part where cable comes out of the magnetic connector, nor putting undue strain where the cable comes out of the heat shrink.
Here's the fixed magnetic connector on an older MacBook:
As you can see, I've heated the sheath shrink so as to produce a little funnel at the end, for further strain relief.
Also, I've gone onto the magnetic connector - previously I had not done that (because the heat shrink was too tick, but instead tried to be as flush as possible). However, with the 4:1 heat shrink, the solution wasn't that good, as it just looked like it added to the strain between cable and magnetic connector. However, with the 3:1 heat shrink this worked. Going over the connector wth the thinner heal shrink does reduce the clearance (obviously), which means the connector doesn't connect as flush as before, but it does work just fine.
With the 3:1 heat shrink the cable also remains fairly flexible, not putting strain onto any one part. The cable going into the PSU was also showing signs of the same wear, so here's the fx:
Given the success of this, it seemed advisable to treat another PSU that were just starting to show similar signs of wear. Here's the fixed PSU of a new MacBook:
The cable was in a much better state, so this was partially preemptively. With this one, I left the previous tape on, near the PSU. Though (see above) in the other case I have removed it first.
Again, this worked nicely. I was initially concerned that heating he cable might cause issues. Particulaly the magnetic connector got quite hot, but none of the PSUs I fixed like this actually broke. One question to ask might be whether Apple couldn't generally apply about £1 worth of extra material to the PSUs, to relieve the strain?
So - not getting your partner/child/parent the new MacBook they had hoped for as an Xmas present? Give them this handy tip instead to make their old one last longer! :)